Ketone resins are known to provide beneficial properties in coatings, such as adhesiveness improvers in paints. Ketone resins are typically applied to substrates as part of an organic solvent based coating formulation. Economics, environmental regulations and safety concerns have encouraged the replacement of volatile organic solvents with water in most industrial processes. However, ketone resins are often difficult to incorporate in water-rich and water-based coating formulations and can not be dispersed in water without the use of special procedures such as those described in U.S. Pat. No. 4,644,028, where the ketone resin is melted, emulsified and dispersed, after a protective colloid is formed with or on the ketone resin. These methods increase cost and can influence the effectiveness of the ketone resin due to the need to employ a colloid forming material. The difficulties with incorporating ketone resins in aqueous dispersions are magnified where the resin is to be co-dispersed with other components such as a wax. Ketone resins are typically incompatible with some conventional components of coating formulations, such as carnauba wax and paraffin wax.
In some industries limits on the ability to disperse ketone resins in water is a problem, particularly where competing products can be made overseas where there are no restrictions on the use of volatile organic solvents to solubilize or disperse ketone resins. For example, in thermal transfer printing, where images are printed by heating precise areas of a print ribbon for transfer of ink to a receiving substrate, it is often desirable to use ketone resins to provide images with enhanced print quality and resistance to smearing and scratching. However, ketone resins have been found to precipitate, even from mixtures of alcohol and water, particularly where carnauba wax is used.
Extensive work has been done to develop water-rich and water-based coating formulations to replace organic solvent-based systems in forming functional layers for thermal transfer ribbons to improve safety, reduce costs and simplify compliance with environmental regulations and restrictions. See, for example, U.S. Pat. No. 4,923,749, issued to Talvalkar. However, effective, simple methods for incorporating ketone resins in aqueous solutions, particularly in combination with carnauba wax, has not been achieved.
Poly(ethylene oxide) is a water soluble polymer with a large number of polar groups. This polymer has been employed in aqueous-based and organic-based coating formulations to enhance the physical properties of the resulting coatings. For example, the use of poly(ethylene oxide) in polymer solutions of polyethylene is said to provide coatings with enhanced scuff resistance, as disclosed in U.S. Pat. No. 4,169,823. In U.S. Pat. No. 4,102,845, the use of low molecular weight poly(ethylene oxide)s in styrene butadiene polymer dispersions is said to form coatings for paper with improved surface characteristics. Poly(ethylene oxide) polymers have also been used to reduce gelling within aqueous solutions (see U.S. Pat. No. 4,396,522 ) and allow the replacement of natural binders with synthetic binders in coatings (see U.S. Pat. No. 4,102,845). These resins have been used in flexographic inks (see U.S. Pat. No. 4,014,833), pressure sensitive adhesives (see U.S. Pat. No. 5,643,992) and functional layers of thermal transfer ribbons.